There have been a number of devices and sealing means used to seal the tubes and shells in tube and shell heat exchangers so that fluid flowing in either medium would not intermingle.
Typically, brazing, welding or roller-expansion methods have been used to seal the tube to tube sheet joints and tube sheet to shell joints in a typical shell and tube heat exchanger. The disadvantages of these sealing methods are: (1) that the individual tubes cannot be easily removed, (2) the shell side cannot be cleaned mechanically, and (3) any use of plastic baffles in the shell may melt during brazing, or welding.
Other methods have been used to compression seal the tubes to the tube sheet, joints and the tube sheets to the shell joints in a typical shell and tube heat exchanger, however none of such prior methods controlled or limited the amount of compression applied to the gaskets. There were several disadvantages to previous methods of compression sealing. One method required the tube sheet to be welded to the shell. This prevented access to the internal shell area for a cleaning or replacement of tube support baffles and allowed tubes to be replaced only singly and by very complicated procedures. Several methods required the presence of internal welded lugs or tube sheet end stops which complicated the removal of tube support assemblies and prevented the use of conventional tube support baffles. Another method required the presence of removable pressure-transfer devices in place of welded lugs and these components obstructed flow in and out of shell and tube nozzles causing wasted energy due to excessive pressure losses. Another method required the use of very close tolerance components to effectively seal the shell wall end section of the shell component.
A final method involved the use of compressible rubber tube gasket and metal tube sheets which suffered from the defect that the degree of compressive force of the rubber gaskets could not be precisely controlled. Too little or too much compression force could cause the seals to fail with the development of leaks. The only control was the torque applied to the bolts which had to be within a specified range. This necessitated more tedious assembly process to prevent failure of the seals. In addition, this method could lead to a bulging deformation of the outer edges of the rubber gaskets, particularly under high compressive forces. This commonly resulted in the use of extended containment straps to attempt to minimize the bulging deformation of the rubber gaskets.